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A case/referent study of the risk of leukemia in electrical workers exposed to magnetic fields was conducted. The cases consisted of 2,355 male residents of Los Angeles County (LAC), California, 20 to 64 years old, who were diagnosed with leukemia between 1972 and 1990. The referents consisted of 67,212 males diagnosed with cancers other than leukemia or central nervous system malignancies. The cases and referents were identified from a population based cancer registry maintained by LAC. The number of subjects employed in eight electrical occupations including electrical engineer, phone line worker and splicer, electrician, and television and radio repairman was determined. Magnetic field exposures were measured for 278 workers employed in the specified electrical jobs and for 105 workers employed in 18 nonelectrical occupations. The magnetic field data were used to create the indices of exposure: mean magnetic field intensity, time above 2.5 milligauss (mG), and time above 25mG. Associations between occupational category and magnetic field exposure index (EI) and leukemia risk were evaluated by case/control techniques. When averaged across all electrical occupations, all magnetic field EIs were significantly greater than those for nonelectrical occupations. When analyzed by job category, all electrical occupations except electrical engineer had greater magnetic field exposures than the nonelectrical occupations. There were 121 leukemia cases diagnosed among workers in electrical occupations and 2,234 in workers in nonelectrical jobs. This yielded a slightly elevated risk for leukemia in the electrical workers, odds ratio (OR) 1.3. The risk for specific leukemia types such as acute and chronic nonlymphocytic leukemia and chronic myeloid leukemia (CML) were similar, ORs 1.2 to 1.3. When stratified by increments of magnetic field exposure, the risk for all leukemias was slightly increased, the ORs per 10mG increase (OR/10mG) ranging from 1.1 to 1.4 for all EIs. A somewhat stronger association was seen for CML, the OR/10mGs ranging from 1.1 to 2.2. The authors conclude that the weak associations found in the study are consistent with other studies that found associations between the job title electrical worker and increased leukemia risk.